1. Field of the Invention
The present invention relates to a pharmaceutical use of FAM19A5 regulating proliferation and differentiation of neural stem cells in vertebrates for diagnosing, preventing, or treating damage to the central nervous system, degenerative brain diseases, or central nervous system diseases.
2. Discussion of Related Art
A neural plate becomes a neural tube during early development, and a cavity within neural tube forms a ventricle through the developmental process. The cell layer closest to the ventricle is the ventricular zone. An additional proliferating cell layer is formed above the ventricular zone through a neurogenesis process, which is referred to as the subventricular zone. Progenitor cells in the ventricular zone and the subventricular zone have properties of neural stem cells and migrate to a cortical plate through a complex control system [Dehay and Kennedy, Nat Rev Neurosci 8:438-450, 2007; Molyneaux et al., Nat Rev Neurosci 8:427-437, 2007; Angevine and Sidman, Nature 192:766-768, 1961; Caviness and Takahashi, Brain Dev 17:159-163, 1995].
Neural stem cells have an ability to divide continuously, that is, a self-renewal ability, and differentiate into neurons, astrocytes, and oligodendrocytes of the central nervous system. The differentiation process into neurons mainly occurs during the embryonic period, but the differentiation process into glial cells occurs after birth [Bayer et al., J Comp Neurol 307:499-516, 1991; Miller and Gauthier, Neuron 54:357-369, 2007].
Differentiation from neural stem cells into neurons and glial cells is a phenomenon that is continuously observed in developmental process of the brain and an adult's brain. In the adult brain, neurogenesis occurs in two different brain regions, the subventricular zone of the lateral ventricle and the dentate gyms of the hippocampus. In the subventricular zone, ependymal cells closest to the ventricle and astrocytes distributed therealong serve as neural stem cells, and the two types of cells become neuroblasts through transient amplifying cells [Doetsch, Curr Opin Genet Dev 13:543-550, 2003; Doetsch et al., Cell 97:703-716, 1999; Lois and Alvarez-Buylla, Proc. Natl. Acad. Sci. USA 90:2074-2077, 1993; Palmer et al., Mol Cell Neurosci 8:389-404, 1997; Temple, Nature 414:112-117, 2001].
In order to maintain normal functions of the brain, a numerical balance of neurons and glial cells is essential. In the past, astrocytes, which accounted for the majority of glial cells, were regarded as merely protective cells that aided neurons in performing their functions. On the contrary, astrocytes are now known to affect the environment around neurons beyond serving as a structural support. That is, astrocytes secrete growth factors, regulate functions of neurons, and help maintain the barrier between blood vessels and the brain. Also, astrocytes are known to play a more active role by directly regulating structure formation and synapse function between neurons [Nedergaard et al., Trends Neurosci 26:523-530, 2003; Ullian et al., Science 291:657-661, 2001; Song et al., Nature 417:39-44, 2002; Temple and Davis, Development 120:999-1008, 1994; Seri et al., J Neurosci 21:7153-7160, 2001; Svendsen, Nature 417:29-32, 2002].
Functional significance of astrocytes is pathologically known through a great deal of research. When the brain is damaged, astrocytes actively proliferate, become reactive, and hypertrophy is observed. Active proliferation of such glial cells is advantageous in that it promotes recovery of tissues shortly after initial damage and prevents damage from spreading. However, when such a phenomenon is repeated, regeneration of neurons is suppressed and an inflammatory response is caused, and damage is applied, which may result in degenerative brain disease [Myer et al., Brain 129:2761-2772, 2006; Chen and Swanson, J Cereb Blood Flow Metab 23:137-149, 2003; Cunningham et al., Brian 128: 1931-1942, 2005; Faden, Curr Opin Neurol 15:707-712, 2002; Katayama et al., J Neurosurg 73:889-900, 1990].
Gliosis is a phenomenon that commonly occurs in various pathological processes of the central nervous system and is caused by hyperproliferation and activation of astrocytes resulting from neuronal damage. When damage is applied to the central nervous system, normal astrocytes become hypertrophic, reactive astrocytes that increase generation of an intermediate filament protein called glial fibrillary acidic protein (GFAP). Various glial cells including reactive astrocytes undergo hyperproliferation after damage and a solid cell layer named a glial scar that is a product of the healing process is formed. Such gliosis is observed in degenerative brain diseases including Huntington's disease, Parkinson's disease, and Alzheimer's disease, in cerebrospinal damage, and various pathological phenomena of the central nervous system such as strokes and brain tumors [Faideau et al., Hum Mol Genet, 2010; Chen et al., Curr Drug Targets, 2005; Rodriguez et al., Cell Death Differ, 2009; Robel et al., J Neurosci, 2011; Talbott et al., Exp Neurol, 2005; Shimada et al., J Neurosci; 2012; Sofroniew and Vinters, Acta Neuropathol, 2010]
In general, gliosis has various influences depending on the circumstances in which damage has initially occurred or the time that has elapsed after a wound has occurred. After damage, initial reactive astrocytes secrete nerve growth factors preventing programmed cell death such as GDNF and cause resumption in the uptake of glutamic acid, thereby protecting neurons. In addition, the initial reactive astrocytes positively function in processes such as recovery of the blood-brain barrier, isolating a region in which damage has occurred, and preventing infection of healthy tissues. However, when a predetermined time elapses after damage, glia scars are formed by hyperproliferated reactive astrocytes and surround a damaged region like a net, and an inhibitory extracellular matrix accumulates. A dense structure of such proteins serves as a barrier that prevents neurons from being physically and chemically regenerated and reconstructing connections. Also, substances that induce inflammation and neurotoxic substances such as cytotoxic cytokines are secreted to induce apoptosis of neurons, inhibit functional recovery, and worsen pathological symptoms. In the related art, central nervous system diseases may be detected through a histopathological test, computerized tomography (CT), or magnetic resonance imaging (MRI). However, diagnosis using such methods may be possible only after the disease has progressed to some extent. Therefore, development of a diagnosis marker that may rapidly and accurately identify the degree of progress of central nervous system disease is essential. Also, a method of treatment in which neurons survive at the early stage of damage and generation of glia scars is minimized and neuron regeneration is promoted at the later phase will be the best method.